Message-ID: <878qmdahbg.fsf@oracle.com>
Date: Fri, 30 May 2025 15:01:55 -0700
From: Stephen Brennan <stephen.s.brennan@...cle.com>
To: Ye Liu <ye.liu@...ux.dev>, akpm@...ux-foundation.org
Cc: linux-debuggers@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-toolchains@...r.kernel.org,
        osandov@...ndov.com, paulmck@...nel.org, sweettea-kernel@...miny.me,
        liuye@...inos.cn, ye.liu@...ux.dev, fweimer@...hat.com, sj@...nel.org
Subject: Re: [PATCH v5] tools/mm: Add script to display page state for a
 given PID and VADDR

Ye Liu <ye.liu@...ux.dev> writes:
> Introduces a new drgn script, `show_page_info.py`, which allows users
> to analyze the state of a page given a process ID (PID) and a virtual
> address (VADDR). This can help kernel developers or debuggers easily
> inspect page-related information in a live kernel or vmcore.
>
> The script extracts information such as the page flags, mapping, and
> other metadata relevant to diagnosing memory issues.
>
> Output example:
> sudo ./show_page_info.py 1 0x7fc988181000
> PID: 1 Comm: systemd mm: 0xffff8d22c4089700
> RAW: 0017ffffc000416c fffff939062ff708 fffff939062ffe08 ffff8d23062a12a8
> RAW: 0000000000000000 ffff8d2323438f60 0000002500000007 ffff8d23203ff500
> Page Address:    0xfffff93905664e00
> Page Flags:      PG_referenced|PG_uptodate|PG_lru|PG_head|PG_active|
>                  PG_private|PG_reported|PG_has_hwpoisoned
> Page Size:       4096
> Page PFN:        0x159938
> Page Physical:   0x159938000
> Page Virtual:    0xffff8d2319938000
> Page Refcount:   37
> Page Mapcount:   7
> Page Index:      0x0
> Page Memcg Data: 0xffff8d23203ff500
> Memcg Name:      init.scope
> Memcg Path:      /sys/fs/cgroup/memory/init.scope
> Page Mapping:    0xffff8d23062a12a8
> Page Anon/File:  File
> Page VMA:        0xffff8d22e06e0e40
> VMA Start:       0x7fc988181000
> VMA End:         0x7fc988185000
> This page is part of a compound page.
> This page is the head page of a compound page.
> Head Page:       0xfffff93905664e00
> Compound Order:  2
> Number of Pages: 4
>
> Signed-off-by: Ye Liu <liuye@...inos.cn>

Reviewed-by: Stephen Brennan <stephen.s.brennan@...cle.com>

>
> Changes in v5:
> - Use platform-aware word-size reads instead of raw byte access.
> - Replace Object() with drgn.cast() for type safety.
> - Better handle memcg flags and error cases.
> - Exit on fatal errors with sys.exit().
> - Remove 'User Virtual Address'.
> - Link to v4:https://lore.kernel.org/all/20250528091543.355386-1-ye.liu@linux.dev/
>
> Changes in v4:
> - Add error and exception handling.
> - Adjust the way to obtain PAGE_SIZE.
> - Fix the acquisition of memcg.
> - Link to v3:https://lore.kernel.org/all/20250423014850.344501-1-ye.liu@linux.dev/
>
> Changes in v3:
> - Adjust display style.
> - Link to v2:https://lore.kernel.org/all/20250421080748.114750-1-ye.liu@linux.dev/
>
> Changes in v2:
> - Move the show_page_info.py file to tools/mm.
> - Link to v1: https://lore.kernel.org/all/20250415075024.248232-1-ye.liu@linux.dev/
> ---
>  MAINTAINERS                |   5 ++
>  tools/mm/show_page_info.py | 169 +++++++++++++++++++++++++++++++++++++
>  2 files changed, 174 insertions(+)
>  create mode 100644 tools/mm/show_page_info.py
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 0cb9e55021cb..3cbd46bf1eab 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -18726,6 +18726,11 @@ F:	Documentation/mm/page_table_check.rst
>  F:	include/linux/page_table_check.h
>  F:	mm/page_table_check.c
>  
> +PAGE STATE DEBUG SCRIPT
> +M:	Ye Liu <liuye@...inos.cn>
> +S:	Maintained
> +F:	tools/mm/show_page_info.py
> +
>  PANASONIC LAPTOP ACPI EXTRAS DRIVER
>  M:	Kenneth Chan <kenneth.t.chan@...il.com>
>  L:	platform-driver-x86@...r.kernel.org
> diff --git a/tools/mm/show_page_info.py b/tools/mm/show_page_info.py
> new file mode 100644
> index 000000000000..c46d8ea283d7
> --- /dev/null
> +++ b/tools/mm/show_page_info.py
> @@ -0,0 +1,169 @@
> +#!/usr/bin/env drgn
> +# SPDX-License-Identifier: GPL-2.0-only
> +# Copyright (C) 2025 Ye Liu <liuye@...inos.cn>
> +
> +import argparse
> +import sys
> +from drgn import Object, FaultError, PlatformFlags, cast
> +from drgn.helpers.linux import find_task, follow_page, page_size
> +from drgn.helpers.linux.mm import (
> +    decode_page_flags, page_to_pfn, page_to_phys, page_to_virt, vma_find,
> +    PageSlab, PageCompound, PageHead, PageTail, compound_head, compound_order, compound_nr
> +)
> +from drgn.helpers.linux.cgroup import cgroup_name, cgroup_path
> +
> +DESC = """
> +This is a drgn script to show the page state.
> +For more info on drgn, visit https://github.com/osandov/drgn.
> +"""
> +
> +def format_page_data(page):
> +    """
> +    Format raw page data into a readable hex dump with "RAW:" prefix.
> +
> +    :param page: drgn.Object instance representing the page.
> +    :return: Formatted string of memory contents.
> +    """
> +    try:
> +        address = page.value_()
> +        size = prog.type("struct page").size
> +
> +        if prog.platform.flags & PlatformFlags.IS_64_BIT:
> +            word_size = 8
> +        else:
> +            word_size = 4
> +        num_words = size // word_size
> +
> +        values = []
> +        for i in range(num_words):
> +            word_address = address + i * word_size
> +            word = prog.read_word(word_address)
> +            values.append(f"{word:0{word_size * 2}x}")
> +
> +        lines = [f"RAW: {' '.join(values[i:i + 4])}" for i in range(0, len(values), 4)]
> +
> +        return "\n".join(lines)
> +
> +    except FaultError as e:
> +        return f"Error reading memory: {e}"
> +    except Exception as e:
> +        return f"Unexpected error: {e}"
> +
> +def get_memcg_info(page):
> +    """Retrieve memory cgroup information for a page."""
> +    try:
> +        MEMCG_DATA_OBJEXTS = prog.constant("MEMCG_DATA_OBJEXTS").value_()
> +        MEMCG_DATA_KMEM = prog.constant("MEMCG_DATA_KMEM").value_()
> +        mask = prog.constant('__NR_MEMCG_DATA_FLAGS').value_() - 1
> +        memcg_data = page.memcg_data.read_()
> +        if memcg_data & MEMCG_DATA_OBJEXTS:
> +            slabobj_ext = cast("struct slabobj_ext *", memcg_data & ~mask)
> +            memcg = slabobj_ext.objcg.memcg.value_()
> +        elif memcg_data & MEMCG_DATA_KMEM:
> +            objcg = cast("struct obj_cgroup *", memcg_data & ~mask)
> +            memcg = objcg.memcg.value_()
> +        else:
> +            memcg = cast("struct mem_cgroup *", memcg_data & ~mask)
> +
> +        if memcg.value_() == 0:
> +            return "none", "/sys/fs/cgroup/memory/"
> +        cgrp = memcg.css.cgroup
> +        return cgroup_name(cgrp).decode(), f"/sys/fs/cgroup/memory{cgroup_path(cgrp).decode()}"
> +    except FaultError as e:
> +        return "unknown", f"Error retrieving memcg info: {e}"
> +    except Exception as e:
> +        return "unknown", f"Unexpected error: {e}"
> +
> +def show_page_state(page, addr, mm, pid, task):
> +    """Display detailed information about a page."""
> +    try:
> +        print(f'PID: {pid} Comm: {task.comm.string_().decode()} mm: {hex(mm)}')
> +        try:
> +            print(format_page_data(page))
> +        except FaultError as e:
> +            print(f"Error reading page data: {e}")
> +        fields = {
> +            "Page Address": hex(page.value_()),
> +            "Page Flags": decode_page_flags(page),
> +            "Page Size": prog["PAGE_SIZE"].value_(),
> +            "Page PFN": hex(page_to_pfn(page).value_()),
> +            "Page Physical": hex(page_to_phys(page).value_()),
> +            "Page Virtual": hex(page_to_virt(page).value_()),
> +            "Page Refcount": page._refcount.counter.value_(),
> +            "Page Mapcount": page._mapcount.counter.value_(),
> +            "Page Index": hex(page.__folio_index.value_()),
> +            "Page Memcg Data": hex(page.memcg_data.value_()),
> +        }
> +
> +        memcg_name, memcg_path = get_memcg_info(page)
> +        fields["Memcg Name"] = memcg_name
> +        fields["Memcg Path"] = memcg_path
> +        fields["Page Mapping"] = hex(page.mapping.value_())
> +        fields["Page Anon/File"] = "Anon" if page.mapping.value_() & 0x1 else "File"
> +
> +        try:
> +            vma = vma_find(mm, addr)
> +            fields["Page VMA"] = hex(vma.value_())
> +            fields["VMA Start"] = hex(vma.vm_start.value_())
> +            fields["VMA End"] = hex(vma.vm_end.value_())
> +        except FaultError as e:
> +            fields["Page VMA"] = "Unavailable"
> +            fields["VMA Start"] = "Unavailable"
> +            fields["VMA End"] = "Unavailable"
> +            print(f"Error retrieving VMA information: {e}")
> +
> +        # Calculate the maximum field name length for alignment
> +        max_field_len = max(len(field) for field in fields)
> +
> +        # Print aligned fields
> +        for field, value in fields.items():
> +            print(f"{field}:".ljust(max_field_len + 2) + f"{value}")
> +
> +        # Additional information about the page
> +        if PageSlab(page):
> +            print("This page belongs to the slab allocator.")
> +
> +        if PageCompound(page):
> +            print("This page is part of a compound page.")
> +            if PageHead(page):
> +                print("This page is the head page of a compound page.")
> +            if PageTail(page):
> +                print("This page is the tail page of a compound page.")
> +            print(f"{'Head Page:'.ljust(max_field_len + 2)}{hex(compound_head(page).value_())}")
> +            print(f"{'Compound Order:'.ljust(max_field_len + 2)}{compound_order(page).value_()}")
> +            print(f"{'Number of Pages:'.ljust(max_field_len + 2)}{compound_nr(page).value_()}")
> +        else:
> +            print("This page is not part of a compound page.")
> +    except FaultError as e:
> +        print(f"Error accessing page state: {e}")
> +    except Exception as e:
> +        print(f"Unexpected error: {e}")
> +
> +def main():
> +    """Main function to parse arguments and display page state."""
> +    parser = argparse.ArgumentParser(description=DESC, formatter_class=argparse.RawTextHelpFormatter)
> +    parser.add_argument('pid', metavar='PID', type=int, help='Target process ID (PID)')
> +    parser.add_argument('vaddr', metavar='VADDR', type=str, help='Target virtual address in hexadecimal format (e.g., 0x7fff1234abcd)')
> +    args = parser.parse_args()
> +
> +    try:
> +        vaddr = int(args.vaddr, 16)
> +    except ValueError:
> +        sys.exit(f"Error: Invalid virtual address format: {args.vaddr}")
> +
> +    try:
> +        task = find_task(args.pid)
> +        mm = task.mm
> +        page = follow_page(mm, vaddr)
> +
> +        if page:
> +            show_page_state(page, vaddr, mm, args.pid, task)
> +        else:
> +            sys.exit(f"Address {hex(vaddr)} is not mapped.")
> +    except FaultError as e:
> +        sys.exit(f"Error accessing task or memory: {e}")
> +    except Exception as e:
> +        sys.exit(f"Unexpected error: {e}")
> +
> +if __name__ == "__main__":
> +    main()
> -- 
> 2.25.1

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